(1) Field of the Invention
The present invention pertains to a spinal needle having a slight curvature at its distal end and a method of using the spinal needle in administering a spinal anesthetic while preventing the development of post dural puncture headache.
(2) Description of the Related Art
Headache continues to be a common complication associated with subarachnoid puncture. The cause of headache pain is believed to be the loss of cerebrospinal fluid from the subarachnoid compartment of the spine, through the puncture site into the epidural compartment of the spine, with a resulting caudal movement of the cranio-spinal contents when the patient subsequently assumes an upright position.
The majority of physicians prefer the use of the midline approach for spinal puncture. Generally, with the midline approach, the spinal injection is made at the center of the patient's back with the needle oriented in a plane parallel to the centerline of the spine. The needle tip is inserted into the back in a straight line toward the midline of the spine between the second 10 and third 12 lumbar vertebrae, a direction generally represented by the arrow (A) shown in FIG. 3.
The applicant administered his first spinal anesthetic employing the midline approach. However, after unsuccessful attempts, a lateral approach, a technique used in difficult situations, was used and was successful on the first attempt. The lateral approach technique was so easy to perform that the applicant has exclusively used this technique with a 20 gauge Becton Dickinson.RTM. (B-D) Quincke point needle. In over twenty years of practice over four thousand spinal anesthetics were performed by the applicant and by resident interns under his close supervision utilizing the lateral approach. The lateral approach differs from the midline approach by the needle being introduced at a point spaced two to three centimeters laterally from the midline of the spine. Due to the lateral positioning, the needle must pass through more muscle tissue before reaching the spine than in the midline approach. All of the over four thousand spinal anesthetics were without headache. The absence of post dural puncture headache led the applicant to study the difference between lateral and midline puncture of the dura mater. This led to the idea that the angle at which the needle pierces the dura and arachnoid membranes, rather than the size of the needle, was the most important factor in the occurrence of post dural puncture headache. The applicant has conducted several different tests in investigating this hypothesis. In the investigations, studies were conducted on two anatomical models--a human dura model and a lumbar spine model--and on an artificial dura model.
In the studies conducted on the human dura model, pieces of lumbar dura with its attached membranes were removed from human cadavers and sealed over a small opening in a section of one inch plastic tubing. The tubing was closed at one end and was connected to a water manometer inserted at its opposite end. The tubing was filled with water tinted with a blue dye. A syringe, filled with the blue tinted water, was attached to the tubing to allow the introduction or removal of water from the tube to vary the water pressure in the manometer. The entire tube and surrounding lumbar dura were emersed in a saline-filled vessel. Pressure in the manometer was set at 200 millimeters and the dura model was ready for several spinal needle puncture tests.
Perpendicular punctures, punctures made at the midline, resulted in a continuous leakage of fluid from the punctures as long as positive pressure existed in the system manometer. After pressure in the manometer was reduced to zero due to the leakage, further repressurization of the "dural space" by injecting additional tinted fluid into the manometer from the syringe caused more leakage to occur.
Resetting the system with 200 millimeters of tinted fluid in the manometer, puncturing the dura at a 35 degree lateral angle from the midline with the bevel of the needle tip facing the dura resulted in total fluid pressure loss in the manometer due to leakage just as in the perpendicular puncture experiments. However, as soon as pressure was reapplied to the system by the syringe, the leakage from the punctures ceased immediately and permanently. Despite any pressure change thereafter, from 0 to 570 millimeters of tinted fluid in the manometer, leakage did not reappear. It was also observed that puncture of the dura at an angle caused the colored fluid to leak in a stream from the puncture at the same angle as the puncture.
The perpendicular puncture and angled puncture experiments were performed on 36 dura specimens with 20, 22 and 25 gauge B-D sharp beveled needles, with a total of 324 punctures.
In the angled puncture experiments, measurements were made of the minimum needle angle to the spine midline necessary to obtain a prompt closure of the valvular opening formed in the dura by the needle tip puncture. These measurements were made with gradually decreasing angles (i.e., gradually approaching perpendicular needle orientation) of the piercing needle in 5 degree increments from 45 degrees. When the needle orientation reached 15, 10 and 5 degrees from the perpendicular with needles of 20, 22 and 25 gauge, constant leakage occurred with positive pressure in the manometer. The leakage still occurred after the initial manometer pressure was allowed to decrease to zero and the manometer was then repressurized by adding additional fluid to the manometer from the syringe. A needle angle of 35 degrees resulted in closure of the valvular flap formed by the punctured opening in all cases.
The results of these tests led to the investigation of the importance of the position of the beveled opening at the needle's tip relative to the dura. Several of the test punctures revealed that perpendicular punctures will leak, regardless of the bevel's rotation and size of the needle.
In conducting the lumbar tissue model experiments, the second and third lumbar vertebrae with the overlying skin, subcutaneous tissue, muscles, interspinous ligaments and dura intact were removed from a cadaver. Needles of various sizes were inserted perpendicularly to the surface at the midline into the subarachnoid space. An x-ray examination in a cranio-caudal direction (in a direction from the head down the length of the spine) was then carried out to determine the exact position of the needles as affected by the direction of the bevel tip. The X-rays indicated that the needle bevel orientation strongly influenced the path traversed by a flexible needle in spinal injections. The X-rays showed that a 20 gauge needle, perpendicularly introduced at the midline, remained in the median plane and entered the subarachnoid space also in the midline. However, thinner gauged needles (22 and 25 gauge) perpendicularly introduced at the midline entered the subarachnoid space in a tangential manner. As the needle was introduced through the tissue toward the subarachnoid space of the spine, the density of the tissue caused the needle's path to bend or curve in a direction opposite to the side faced by the bevel. A 22 gauge needle introduced at the midline with its bevel facing to the left curved to the right as it passed through the tissue. A 25 gauge needle introduced at the midline and with its course guided by a 21 gauge introducer also curved in a direction opposite to the side faced by the bevel.
In the experiments conducted on the artificial dura model, a one-inch thick "dura" was constructed from an elastic dental impression powder. This model was used to illustrate the characteristics of the three primary modes of needle bevel penetration through the dura. A schematic representation of the dura model 14 used is shown in FIG. 5. This model shows the characteristics of dural punctures with sharp beveled needles, emphasizing the differences in the valvular flap openings cut through the dural mater by the needle opening beveled edge from the primary modes of perpendicular and tangential puncture of the dura.
At the left side in FIG. 5, a perpendicular puncture of the dura 14 results in a swinging-door-like valvular flap 16 formed in the dura by the bevel opening edge 18 of the needle 20. The valvular flap 16 of this type can remain open by the pressure of the cerebrospinal fluid, which is constantly present in the subarachnoid space 22 and can be reproduced by the physical activity of the patient, and by negative epidural relative pressure in the epidural space 24. With the valvular flap 16 formed by the perpendicular puncture being capable of swinging to either the subarachnoid side 22 of the puncture or the epidural side 24 of the puncture, the probability of cerebrospinal fluid leakage is high and the probability of resulting headache is high.
The puncture shown at the center of the dura model 14 in FIG. 5 is made with the needle 20' oriented at an angle relative to the dura 14 with the bevel opening 18' of the needle facing away from the dura and toward the operator making the injection. The valvular flap 16' formed by the needle in the dura mater is able to deflect into the epidural space 24. With this type of puncture opening, cerebrospinal fluid leakage may be maintained by both subarachnoid positive pressure of the fluid and epidural negative pressures. With this particular type of puncture, pressure from outside the valvular flap in the epidural space 24, in the form of an epidural saline or blood patch, may help to seal off the opening as the subarachnoid and epidural spaces reach equilibrium pressure.
The right side of FIG. 5 illustrates the dura puncture mode which results in the least leakage or no leakage of cerebrospinal fluid through the puncture opening. The valvular flap 16" formed by the puncture is made by the bevel opening 18" of the needle 20" facing the dura 14. This flap 16" will be able to close itself by means of increased cerebrospinal fluid pressure in the subarachnoid space 22 from restitution of the fluid and/or early ambulation, cough, stretching, or some other physical activity of the patient.
The above studies suggested to the applicant that a tangential puncture, with the needle bevel opening facing the dura, is the most critical factor in avoiding post dural puncture headache. The importance of the bevel position is most appreciated after the needle is withdrawn from the dura and the healing process begins to take place. At first there will be an uncontrollable cerebrospinal fluid escape through the puncture, until pressure equilibrium is established between the subarachnoid and epidural spaces. Fluid will flow from a high pressure area as long as positive pressure exists and an escape route is open. The flow of cerebrospinal fluid after every dural puncture is a definite impediment to wound healing. However, after a momentary equilibrium in fluid pressure is reached between the subarachnoid and epidural spaces, the valvular flap formed by the puncture of the type shown at the right in FIG. 5 will close from the increasing pressure of cerebrospinal fluid restitution resulting from the patient's physical activity, and the valvular flap will not reopen, thus preventing headache. The role of cerebrospinal fluid in terms of its replacement capacity is important (500 ml per 24 hours, or more) in providing the closing force on the valvular opening 16" of the tangential dural puncture. The closing force on the valvular opening is directly proportional to the area of the valvular flap (force=pressure.times.area). Enlarging the valvular opening by using a large needle will increase the cerebrospinal fluid pressure on the valve surface and close the valve forcefully. The larger needle will also deviate less and allow greater control and more accurate placement of the puncture.
Since the density and depth of the material through which the beveled needle travels determines the degree of bending, even midline punctures can and will enter the dura somewhat as though they were done with a lateral approach with the bevel facing the dura. However, since finer bevel needles cannot be controlled as well as large needles in terms of dura entry point (or even dura entry itself), it seemed to the applicant reasonable to reexamine the use of larger beveled needles with the lateral approach.
From the applicant's investigations, it was determined that it was desirable to use a larger needle (20 gauge needle) in spinal injections because the larger needle would deviate less and allow greater control and a more accurate placement of the puncture. Also, the larger needle creates a larger valvular flap opening as it punctures the dura. The larger valvular flap will increase the pressure of cerebrospinal fluid on the valve surface and close the valve forcefully once the needle is withdrawn and the presence of cerebrospinal fluid reaches an equilibrium across the puncture opening. The midline approach is also preferable over the lateral approach. However, using a larger needle with the midline approach may result in the deflection of the needle being insufficient to penetrate the dura at the optimal angle of at least 35 degrees.
It is, therefore, an object of the present invention to provide an improved spinal injection needle, preferably used in the midline approach, where the needle is specifically designed to penetrate the dura with its bevel opening facing the dura and with the incident angle of the needle being at least the optimal angle of 35 degrees. It is also an object of the invention to provide an improved spinal injection needle where the needle is specifically designed to penetrate the yellow ligament of the spine and the needle tip enter the epidural space without penetrating the dura. It is also an object of the present invention to provide methods of using the needles of the invention in spinal injections avoiding the development of post dural puncture headache.